Character multiplex broadcasting is a system wherein picture information comprising characters and drawings as well as accompanying voice are converted into a format of digital signals before being multiplexed with the conventional video signal for transmission to a television receiver of the general user. The multiplexed signal is demodulated by the television receiver for displaying the picture information on an image receiving tube and outputting the accompanying voice to a speaker.
In particular, such a system is known in the U.S.A. as a closed caption for multiplexing character information with a video signal and displaying the character information as information added to pictures as captions. It is an object of the closed caption to allow a person who has difficulty in hearing to understand a broadcast as a normal person does. The system also provides various general information such as a weather forecast and sport news by virtue of character information appended to a picture signal along with accompanying voice.
A special decoder, that is, a closed-caption decoder is required for extracting character information multiplexed with a video signal as described above out off the multiplexed signal. The closed-caption decoder is abbreviated hereafter as the CCD. However, there are currently only a few television receivers in which a CCD is embedded therein at manufacture. In general, it is therefore necessary to purchase a decoding apparatus with a CCD embedded therein in addition to the television receiver. As a result, the CCD has not come into wide use as fast as expected. In order to solve the problem, a bill requiring that each television receiver sold or manufactured domestically after Jul. 1, 1993 be equipped with a closed-caption decoder (CCD) was passed in the U.S.A. Television sets incorporating such CCD are now available (for example the SONY.RTM.KV32TS36.)
To be sure, it is believed that there are only few cases in which the general consumer requires a CCD. The EIA (Electronic Industry Association) in EIA-608 and the consumer and producer/manufacturer groups propose that a vertical blanking period, a currently unused portion of a planned video signal, be used for a CCD system. It should be noted that the video signal is planned for use to provide extended data services (EDS) to people constituting the majority of the population.
In addition, other independent data services such as StarSight, Telidon and World Teletext Services also use the vertical blanking period of the video signal. For all the services described above, a television receiver equipped with a tuner capable of tuning to a station broadcasting desired data is therefore required.
As implied in the description given so far, some even and odd scan lines in the vertical blanking period, from the 1st to the 21st, are not used. In the closed-caption system, data is multiplexed onto the 21st scan line, line 21 of the unused odd field.
A rough configuration of the conventional television receiver is shown in FIG. 2. FIG. 2 is a block diagram showing the configuration of the conventional television set which is equipped with a closed-caption decoder (CCD). Reference numeral 1 shown in the figure is a main tuner for receiving a radio wave RF1 or a video signal V1 from an antenna. In accordance with a station-select signal S 1 from a video switch 3 to be described later, the main tuner 1 extracts a video signal with an intermediate frequency of a predetermined channel, supplying the signal to the video switch 3 as a video signal V3.
Reference numeral 2 is an auxiliary tuner. Much like the main tuner 1, the auxiliary tuner 2 is used for receiving the radio wave RF1 or the video signal V1 from the antenna. However, the auxiliary tuner 2 works independently of the main tuner 1. Likewise, in accordance with a station-select signal S2 from a microprocessor 9 to be described later, the auxiliary tuner 2 extracts a video signal with an intermediate frequency of a predetermined channel, supplying the signal to the video switch 3 as a video signal V4.
The video switch 3 provides the main tuner 1 described above and a video processor to be discussed later with the station-select S1. At the same time, the video switch 3 is controlled by a signal S3 output by the microprocessor 9 to select two from a plurality of video signals: V2, V3 and V4. As shown in the figure, the video signal V2 is a signal supplied directly from an external source. Two signals V5 and V6 are selected by the video switch 3 to be displayed on main and auxiliary screens respectively. The selected video signal V5 to be displayed on the main screen is supplied to a Y/C separator 4. The selected video signal V6 to be displayed on the auxiliary screen is, on the other hand, supplied to a picture-in-picture (PinP) circuit 5. The PinP circuit 5 may also be referred to hereafter as a picture-out-picture or picture-outside-picture (PoutP) circuit. Such PinP and PoutP circuits and the like may be collectively referred to generically herein as a multiple picture processor.
The Y/C separator 4 extracts luminance (Y) and chrominance (C) signals YCS from the video signal V5. The signals YCS are supplied to a video processor 6. The Y/C separator 4 also provides a CCD/EDS data extractor (decoder) 7 with an NTSC-system color-TV signal TVS. Thus, the decoder 7 always operates on the signal from the main video signal V5.
The PinP (PoutP) circuit 5 carries out predetermined processing on the video signal V6 supplied thereto in accordance with the size of the auxiliary screen and the display position, outputting the processed signal to the video processor 6.
Then, the video processor 6 mixes the video signals output by the Y/C separator 4 for the main screen and a video signal output by the PinP circuit 5 for the auxiliary screen. The mixed signal is supplied to an RGB switch 8 as an RGB signal.
The CCD/EDS data extractor 7 includes an embedded a data processor (or a data slicer) for extracting a caption signal from the NTSC-system color-TV signal TVS. The extracted caption signal is decoded by means of a decoder also embedded therein. Furthermore, the CCD/EDS data extractor 7 supplies a decoded result to the RGB switch 8 as a display character signal, another RGB signal, which is synchronized with a vertical/horizontal synchronization video signal.
The RGB switch 8 mixes the RGB signal comprising the video signals for the main and auxiliary screens with the other RGB signal, the caption (characters to be displayed) signal output by the CCD/EDS data extractor 7, to produce a final RGB signal. The final RGB signal is supplied to a CRT 10 for displaying video information and captions conveyed by the final RGB signal.
As described above, in the aforementioned configuration of the conventional TV receiver, the video signal V3 selected by the main tuner 1 is displayed on the main screen. The video signal V4 selected by the auxiliary tuner 2 as an auxiliary-screen signal is processed by the picture-in-picture circuit 5 and mixed with the luminance and color signals YCS by the video processor 6 before being displayed. The CCD/EDS data extractor 7 extracts a caption signal supplied along with the video signal for the main screen. The caption signal is extracted from the color-television signal TVS for the main-screen video signal provided to the CCD/EDS data extractor 7. The caption signal is decoded by the CCD/EDS data extractor 7 before being displayed on the CRT 10. Of course, the video signals for the main and auxiliary screens can be swapped with each other. In addition, it is also possible to display the electric wave RF2 input from an external source as a main or auxiliary-screen signal.
In the case of the conventional TV receiver described above, no problem is encountered as long as the user does not change the channels once selected for a television program and a data service. If the user switches the channel from a television program watched so far to another, however, the data service watched so far cannot be seen anymore even if the user desires to. This is because, every time the user changes the channel for the main screen, the channel for the data service is also changed. That is to say, the conventional TV receiver has a problem that a desired data service cannot be independently specified.
The problem described above is caused by the fact that the conventional TV receiver is designed so that only the CCD and the extended data services can be decoded. To be more specific, the conventional TV receiver allows only CCD and extended data services included in a selected video signal currently being watched to be received. As a result, with the conventional TV receiver, a data service of a specific or arbitrary channel cannot be received, giving rise to a problem that CCD data and/or EDS information from another video-signal source cannot be decoded even if the other video-signal source can be selected independently.
It is an object of the present invention to provide a TV receiver which can selectively receive additional information multiplexed in a video signal from a video-signal source different from the one currently being watched.